The present invention relates to a construction method for boring a large-section tunnel safely and quickly by reinforcing and improving the ground surrounding the tunnel to develop artificial ground arches.
A construction method for boring a tunnel through weak ground by reinforcing the ground to increase its capability of self-support and prevent the tunnel from collapsing is shown in publication of patent application JP-1989-137094.
In this prior art, injection holes are drilled from the face of the tunnel into the ground surrounding the tunnel toward the tunneling direction. Then injection pipes are inserted into the drilled holes to inject grout into the injection holes for reinforcing the ground surrounding the tunnel. After the ground is reinforced, the reinforced part of the ground is excavated, and timbered and/or lined. The steps stated above are repeated to bore the tunnel.
In this prior construction method, however, drilling and injecting steps for reinforcing the ground, and excavating and lining steps for tunnel boring have to be repeated one after another at the face, so that the construction works are complicated and inefficient which result in a longer construction period.
An object of the present invention is to provide a construction method for boring a large-section tunnel safely and quickly by reinforcing and improving in advance the ground over the full length of the tunnel section.
In the sardine-bone construction method for large-section tunnel (SBR Construction Method) of the present invention, for solving the problem stated above, drifts are bored through the full length of the tunnel section, then curved holes inclined in forward or backward directions at an angle of about 45 degrees are drilled at preset intervals from the drifts along the peripheral edges of the sections of the tunnel by using ordinary small bore rock drills and curved steel pipes, the steel pipes are pulled off after injection pipes are inserted into the drilled holes, grout is injected into the ground surrounding the tunnel through the injection pipes to develop artificial ground arches, then the tunnel is excavated, suspension forms are advanced and concrete is placed for secondary lining, whereby the tunnel is bored.
In the construction method, at first, drifts are quickly bored through the full length of the tunnel section. Then curved holes are drilled by using rock drills and curved steel pipes, the steel pipes are pulled off after injection pipes are inserted into the drilled holes, grout is injected into the ground surrounding the tunnel through the injection pipes. Because these steps are executed from the drifts, the works are efficiently completed. It is different from doing the works at the face at intervals of excavating.
In addition, drilling curved holes and injecting grout can be simultaneously executed at more than one places so that the artificial ground arches are quickly developed, since the steps of reinforcing and improving ground are executed after the drift is bored through the full length of the tunnel.
At the face, only excavating and lining steps are continuously executed, so that the boring works are uncomplicated and efficient.
A top drift is suitable for developing artificial ground arches when the tunnel is bore d by adopting an upper half section advancing excavation method.
If drifts are placed in the middle of the side-walls of the tunnel, curved holes are drilled upward along the peripheral edges of the section of the tunnel from the drifts to the top of the tunnel. This is suitably used for excavating upper half unit of the tunnel through weak ground.